For the last 11 years [Gunnar Kanold] has run the annual BASIC 10 Liner contest, and the rules for the 2021 edition are now available. There are four categories and each category has specific definitions of what constitutes a line. All entries must run on an 8-bit computer system that can be emulated.
The first three categories are for games but differ in the line length allowed. You can elect to compete with 80 character lines, 120 character lines, or 256 character lines. There’s also a category for demos, tools, and other applications that must constrain lines to 256 characters.
There are some common-sense rules, of course. You can’t load other programs or data from mass storage. You can’t use machine language or self-modifying code.
If you want to participate, you’ll need to submit your entry by March 27th and the results will be revealed on April 10th. If you need inspiration, look at some of the entries from last year, including Bomb Catcher, Ainvader, and Asteroid.
This is a good excuse to dust off your last retrocomputer project or replica. Seems like you’d want a BASIC that at least let you put multiple statements on a line, though, so probably don’t want to go back too far. Of course, you can always work on your favorite emulator, if you don’t have any hardware.